Psychological stress is associated with a variety of major chronic health disorders and cardiovascular diseases and quantitatively measuring stress aids in stress management, which is essential to maintaining a low stress level. Conventionally, there are two types of psychological stress: acute stress and chronic stress. Acute stress is characterized by rapid changes in the autonomic nervous system that ready the body for “fight or flight” responses to external stimuli. Chronic stress is characterized by prolonged exposure to stressful stimuli which leads to long-term sympathetic overactivity.
Conventional methods of measuring stress calculate heart rate (HR) and heart rate variability (HRV) in the time and frequency domains. However, HR, HRV are highly variable between people. This variability limits the continuous monitoring and accurate measuring of a person's psychological stress levels. Therefore, there is a strong need for a cost-effective solution that overcomes the above issue by adaptively measuring individualized physiology. The present invention addresses such a need.